1. Field of the Invention
This invention relates to electrical connections, and, more particularly, to a connection between an aircraft igniter cable and the exciter driving the igniter.
2. Summary of the Background Art
An aircraft turbine engine is typically provided with two igniter plugs, located in separate combustion chambers, which are used to start the engine, and, in the event of a flame-out, to restart the engine. A typical ignition system for an aircraft turbine engine includes an electrical power source, two igniter plugs, separate exciters for the two igniter plugs, and associated wiring with igniter cables forming high tension leads. Normally, the electrical current driving the igniter is supplied only for a short time when the engine is started.
Each of the exciters converts low voltage alternating or direct current into a high voltage used to drive the associated igniter plug. For example, within the exciter, a 400-Hz alternating current at a low voltage is driven through a primary winding of a power transformer to be transformed into a higher voltage at the secondary winding of the transformer. This higher voltage is then applied to a voltage doubler circuit including a pair of solid state rectifiers and a pair of capacitors. The output of the voltage doubler circuit is applied across the terminals of a storage capacitor, so that with each change in polarity of the alternating current, a pulse of direct current is driven into the storage capacitor, which then assumes an ever increasing charge and voltage level with successive pulses. The high voltage terminal of the storage capacitor is connected to an input of a discharge tube, so that, when the voltage of the storage capacitor reaches a predetermined level of about 3000 volts, the spark gap within the discharge tube breaks down, causing a portion of the charge accumulated within the storage capacitor to flow through the primary winding of a high-tension transformer. The output coil of the high-tension transformer is connected to the igniter plug through a high-voltage output terminal of the exciter and through the igniter cable. When the charge accumulated in the storage capacitor flows through the input coil of the high-tension transformer, a voltage established within the output coil of this transformer causes air within the air gap of the igniter plug to ionize at approximately 26,000 volts, making the gap conductive, so that the remaining electrical charge produces a high current, low voltage spark across the gap. Thus, the connection between the exciter and igniter cable must withstand the application of a voltage over about 26,000 volts to the conductors within the connection, so that current does not flow between these conductors and nearby grounded surfaces, and must additionally be capable of carrying a high current to sustain the spark within the igniter plug gap.
FIG. 1 is an exploded, partly sectional, elevation of elements forming a first version 10 of a conventional connector at an end of an igniter cable for attachment of the cable to the high voltage output terminal of an exciter. The connector 10 includes a terminal 12 crimped in place over the conductor 14 within a wire 16, together with a contact sleeve 18 that is crimped over a sleeve receiving section 20 of the terminal 12. The contact sleeve 18 includes one or more cantilever spring members 22 that are formed inward to make contact with a rounded pin (not shown) within the high voltage terminal of the exciter. The connector 10 additionally includes an insulating sleeve 24 pulled over the contact sleeve 18, the terminal 12, and the end of the wire 16.
When the connector 10 is attached to the high voltage output terminal of the igniter, an axial engagement force pushing the contact sleeve 18 in the direction of arrow 26 is established by contact between the rounded pin within the output terminal and the spring members 22 of the contact sleeve 18. The crimped connection between the contact sleeve 18 and the terminal 12 must be strong enough to resist this axial engagement force, and the assembly including the contact sleeve 18, the terminal 12, and the wire 16 must be held tightly enough within the insulating sleeve 24 to prevent the movement of this assembly in the direction of arrow 26 within the insulating sleeve 24 due to this axial engagement force. Meeting these requirements has resulted in a connector configuration that is often too long to fit within the distance available between the high voltage output terminal of an exciter and an igniter plug without coiling or curving the igniter cable backward to fit on the igniter plug. Thus, what is needed is an igniter cable connector having a robust connection between flexible contact members and the conductor within the wire in a shorter space.
FIG. 2 is an exploded, partly sectional, elevation of elements forming a second version 30 of a conventional connector at an end of an igniter cable for attachment of the cable to the high voltage output terminal of an exciter. The connector 30 includes a terminal 32 crimped in place over the conductor 34 within a wire 36. The terminal 32 includes one or more cantilever spring members 38 and a retaining slot 40. After an insulating sleeve 42 is installed over the terminal 32 and the end of the wire 36, a retaining clip 44, in the form of a snap ring, is snapped into place within the retaining slot 40. This retaining clip 44, through contact with a wall surface 46 of a cavity 48 at an end of the insulating sleeve 42, prevents movement of the terminal 32 in the direction of arrow 50 within the insulating sleeve 42 as the connector 30 is attached to the high voltage output terminal of an exciter, with the cantilever spring members 38 moving in contact with the rounded pin (not shown) within the output terminal.
While the second version 30 of a conventional connector is shorter in length than the first version 10, the retaining clip 44 may become loose due to vibration and may break or fall off when the connector 30 is removed from the high voltage output terminal of the exciter during a maintenance procedure. Such a small part may present a hazard if it is not noticed or otherwise lost within the engine compartment during maintenance. Therefore, what is needed is connector occupying a short space while requiring the use of a retaining clip to be held in place within an insulating sleeve.